Fuel supply system

Abstract

A fuel supply system includes a metering and splitting arrangement receiving a fuel flow and controllably meters and splits the received fuel flow into metered pilot and mains flows for injecting at injector pilot and mains fuel discharge orifices to perform combustor staging control. The system includes mains isolation valves and a mains fuel distribution pipework has fuel lines connected to one of the orifices and extending therefrom to a respective one of the valves. Each valve has a closed position for removing the mains fuel from its injector through its line when the mains distribution pipework is deselected for pilot-only operation, and isolates its line from the metering and splitting arrangement. Each valve has an open position for refilling its injector with mains fuel through its line when the mains distribution pipework is selected for pilot and mains operation, and reconnects its line to the metering and splitting arrangement.

What is claimed is: 
     
         1 . A fuel supply system for fuel injectors of a multi-stage combustor of a gas turbine engine, the fuel supply system including:
 a metering and splitting arrangement which receives a fuel flow and controllably meters and splits the received fuel flow into metered pilot and mains flows for injecting respectively at pilot and mains fuel discharge orifices of the injectors to perform staging control of the combustor; and   pilot and mains fuel distribution pipeworks respectively distributing fuel from the metering and splitting arrangement to the pilot and mains discharge orifices;   wherein the metering and splitting arrangement is operable to select the pilot distribution pipework and deselect the mains distribution pipework for pilot-only operation in which there is a pilot supply to the combustor but no mains supply to the combustor from the injectors, and is operable to select both the pilot and mains distribution pipeworks for pilot and mains operation in which there are pilot and mains supplies to the combustor from the injectors;   wherein the fuel supply system further includes plural mains isolation valves and the mains fuel distribution pipework has plural fuel lines each of which is fluidly connected to a respective one of the mains fuel discharge orifices and extends therefrom to a respective one of the isolation valves;   wherein each isolation valve has a closed position in which it removes the mains fuel from its injector through its fuel line when the mains distribution pipework is deselected for pilot-only operation, and fluidly isolates its fuel line from the metering and splitting arrangement; and   wherein each isolation valve has an open position in which it refills its injector with mains fuel through its fuel line when the mains distribution pipework is selected for pilot and mains operation, and reconnects its fuel line to the metering and splitting arrangement.   
     
     
         2 . A fuel supply system according to  claim 1 , wherein the pilot fuel distribution pipework includes a pilot fuel manifold distributing fuel from the metering and splitting arrangement to the pilot discharge orifices. 
     
     
         3 . A fuel supply system according to  claim 1 , wherein the metering and splitting arrangement includes: a metering valve which receives and controllably meters the fuel flow, and a splitting unit which receives the metered flow from the metering valve and controllably splits the metered flow into the pilot and mains flows. 
     
     
         4 . A fuel supply system according to  claim 1 , wherein each isolation valve in its closed position also removes mains fuel from a portion of its fuel line adjacent its injector, and in its open position refills said portion of its fuel line with mains fuel. 
     
     
         5 . A fuel supply system according to  claim 1 , wherein each fuel line has a top portion at an end thereof and a bottom portion at an opposite end thereof, and is routed such that its injector is at the top end and its isolation valve is at the bottom end. 
     
     
         6 . A fuel supply system according to  claim 1 , wherein each isolation valve has:
 a valve housing which forms an inlet to the mains distribution pipework between the isolation valve and the metering and splitting arrangement, and which forms an outlet to the fuel line of the isolation valve; and   a piston which is slidably movable in the housing between first and second end positions which respectively correspond to the closed and open positions of the valve;   wherein the housing and the piston are configured such that in the second end position of the piston the inlet and the outlet fluidly communicate with each other, and such that in the first end position of the piston a fluid tight seal is formed between the inlet and the outlet.   
     
     
         7 . A fuel supply system according to  claim 6 , wherein:
 each isolation valve has a variable volume, fuel storage sink which is in fluid communication with the outlet, the volume of the sink being at its greatest when the piston is in its first end position, and being at its smallest when the piston is in its second end position; and   the housing and the piston are configured such that, at an intermediate position of the piston, the inlet is substantially closed off by the piston, whereby on moving from its intermediate position to its first end position, the piston draws mains fuel in the fuel line into the sink through the outlet, thereby removing the mains fuel from the injector, and whereby on moving from its first end position to its intermediate position, the piston pushes fuel stored in the sink into the fuel line through the outlet, thereby refilling the injector with mains fuel.   
     
     
         8 . A fuel supply system according to  claim 6 , wherein the piston of each isolation valve is spring biased towards its first end position. 
     
     
         9 . A fuel supply system according to  claim 6 , wherein the movements of the pistons of the isolation valves are hydraulically controlled, and the fuel supply system further includes a solenoid or servo valve which sets the hydraulic fluid control pressure. 
     
     
         10 . A fuel supply system according to  claim 6 , wherein the movements of the pistons of the isolation valves are hydraulically controlled by fuel pressure, 
     
     
         11 . A gas turbine engine having a multi-stage combustor and the fuel supply system according to  claim 1  for supplying fuel to and performing staging control in respect of pilot and mains fuel discharge orifices of fuel injectors of the combustor.